Evidence that termination of the estradiol-induced luteinizing hormone surge in women is regulated by ovarian factors

Abstract

Background: The endogenous LH surge is the result of the estrogen-positive feedback effect. However, the factors that are responsible for the termination of LH surge are not known. Objective: The objective of the study was to investigate the mechanism that terminates the LH surge in women. Subjects and Methods: Eight normally cycling women (aged 42-48 yr) were investigated in two cycles, i.e. cycle 1 (control) and cycle 2. In cycle 2 total abdominal hysterectomy plus bilateral salpingooophorectomy was performed on d 3. In both cycles, estradiol was administered transdermally at the dose of 100 mu g on d 3 and 150 mu g on d 4 and 5. Blood samples were obtained every 12 h from d 3 to 5 and every 6 h thereafter until d 9. Results: In both cycles, after suppression of gonadotropins, the women displayed an endogenous LH surge. The time intervals between the commencement of estradiol treatment and the LH surge onset (73.5 +/- 1.5 vs. 76.5 +/- 2.5 h) and peak LH values (11.4 +/- 1.9 vs. 12.4 +/- 3.1 IU/liter) were comparable in the two cycles (mean +/- SEM). After peaking, LH values decreased gradually in cycle 1, whereas in cycle 2 they remained stable and were higher than the corresponding values in cycle 1 (P < 0.05). Before the LH surge onset, estradiol values showed in both cycles a preovulatory pattern of changes, but starting 24 h after the onset of the LH surge, they were lower in cycle 2 (P < 0.05). Progesterone levels were similar in both cycles until the day of the LH surge onset, but in cycle 2 they declined thereafter and were lower than in cycle 1 (P < 0.05). Conclusions: It is suggested that ovarian factors rather than exhaustion of pituitary reserves are important for termination of the endogenous LH surge during the normal menstrual cycle.